1. Field of the Invention
The present invention relates to a projection image display device that displays a projection image on a screen and a projection optical system used in the projection image display device.
2. Description of the Related Art
In recent years, as a projection image display device that displays a projection image on a screen, a projector device is widely available. In particular, in recent years, there is an increasing demand for a front-projection projector device of a super-wide angle type capable of performing a displaying operation on a large screen with a small projection space. A front-projection projector device of a super-wide angle type is used because projection can be performed on a large screen in a limited space by driving it in obliquely and at a wide angle with respect to the screen.
However, if the projector device is, for example, a super-wide angle type in which a super-wide angle is approximately 70 degrees in terms of a half angle of view, an image size, an image position on the screen, etc., are greatly changed when the distance between the projector device and the screen is only slightly changed.
For example, as shown in FIG. 87, a light ray is incident upon a screen at an angle θ. If a distance measured perpendicular to an in-plane of the screen is changed by only L, a displacement amount x of a position of the light ray that is incident upon the screen is proportional to tan θ. If the projector device is not a super-wide angle type, the angle θ is approximately 20 degrees. In contrast, if the projector device is a super-wide angle type, the light ray is incident upon the screen at the angle θ of around 70 degrees. Therefore, a sensitivity ratio is approximately 7.5× (=tan 70°/tan 20°). Therefore, for the projector device of a super-wide angle type, when, in adjusting a setting position of the projector device in accordance with a projection surface, the distance between the projector device and the screen is only slightly changed, for example, the image position is greatly changed.
Such a problem in which, for example, the image position is changed may be overcome by making use of a screen shift function and a magnification changeover function in a projection optical system. That is, as shown in FIG. 88, an optical-axis position of a projection optical system PJ is moved perpendicularly to a position of an image modulating element P, to move a screen position on a screen SCR.
More specifically, a projection image display device including a relay optical system (which has a magnification changeover function) and an aspherical reflecting mirror (which performs extended projection at an image-formation screen of the relay optical system) and realizing a screen shift function by moving the entire relay optical system is proposed. (Refer to, for example, Japanese Unexamined Patent Application Publication No. 2007-11248 (Patent Document 1).)
In addition, another display device making use of an fθ optical system, including a refracting system and a plurality of free-form surfaces, including a plane reflecting surface at an exit pupil surface of the refracting system, and realizing a screen shift function by rotating the plane reflecting surface is proposed. (Refer to, for example, Japanese Patent No. 4086686 (Patent Document 2).)
Further, still another display device that achieves a screen shift function by moving an image modulating element when a screen is moved during magnification change or by inserting a parallel plate between a projection optical system and the image modulating element and tilting the parallel plate is proposed. (Refer to, for example, Japanese Unexamined Patent Application Publication No. 185709 (Patent Document 3).)